function SelectMainBg() {
	var imgList = new Array(
		"./img/bg_main1.jpg",
		"./img/bg_main2.jpg",
		"./img/bg_main3.jpg",
		"./img/bg_main4.jpg",
		"./img/bg_main5.jpg",
		"./img/bg_main6.jpg",
		"./img/bg_main7.jpg",
		"./img/bg_main8.jpg",
		"./img/bg_main9.jpg"
	);
	var index = Math.floor(Math.random()*10) % imgList.length;
	var mainDiv = document.getElementById("main");
	mainDiv.style.backgroundImage = "url(" + imgList[index] + ")";
	mainDiv.style.backgroundRepeat = "no-repeat";
}